pythonic way to rewrite an assignment in an if statement

Question

Is there a pythonic preferred way to do this that I would do in C++:

for s in str:
    if r = regex.match(s):
        print r.groups()

I r

Answer 1

Perhaps it's a bit hacky, but using a function object's attributes to store the last result allows you to do something along these lines:

def fn(regex, s):
    fn.match = regex.match(s) # save result
    return fn.match

for s in strings:
    if fn(regex, s):
        print fn.match.groups()

Or more generically:

def cache(value):
    cache.value = value
    return value

for s in strings:
    if cache(regex.match(s)):
        print cache.value.groups()

Note that although the "value" saved can be a collection of a number of things, this approach is limited to holding only one such at a time, so more than one function may be required to handle situations where multiple values need to be saved simultaneously, such as in nested function calls, loops or other threads. So, in accordance with the DRY principle, rather than writing each one, a factory function can help:

def Cache():
    def cache(value):
        cache.value = value
        return value
    return cache

cache1 = Cache()
for s in strings:
    if cache1(regex.match(s)):
        # use another at same time
        cache2 = Cache()
        if cache2(somethingelse) != cache1.value:
            process(cache2.value)
        print cache1.value.groups()
          ...